OP0068 DISTINCT STROMAL AND IMMUNE CELL INTERACTIONS SHAPE THE PATHOGENESIS OF RHEUMATOID AND PSORIATIC ARTHRITIS

Background

Rheumatoid (RA) and psoriatic arthritis (PsA) are common autoimmune and autoinflammatory diseases of unknown aetiology characterised by complex synovial pathology with a detrimental effect on the patient’s quality of life. Significant differences in pathophysiology may explain distinct clinical manifestations and account for differential responses to specific therapeutics. Recent implementation of single cell transcriptomic analysis of sorted synovial cells has revealed the diverse cellular landscape of the RA synovial stromal and immune cell compartments, however, a complete analysis of immune and stromal cells in tandem, for RA and PsA patient synovial tissue has not been performed.

Objectives

To combine novel scRNA transcriptomic approaches and ex vivo assays in order to: identify differences in the cellular landscape of RA and PsA synovial tissue inflammation and immune – stromal cell interactions that drive pathology in RA and PsA.

Methods

Single cell transcriptomic profiling of 178,000 synovial tissue cells from 5 PsA and 4 RA patients, importantly, without prior sorting of immune and stromal cells. This approach enabled the generation of a unique cell atlas of intact synovial tissue identifying immune and stromal cell interactions. State of the art data integration and annotation techniques identified and characterised 18 stromal and 14 immune cell clusters. Bioinformatic examination of cell-cell communication via construction of receptor-ligand interaction networks with further in vitro validation of stromal and immune cell crosstalk through flow cytometric analysis, multiplex ELISA and mitochondrial and single cell metabolic profiling by multiphoton and florescent lifetime imaging microscopy, seahorse.

Results

Following quality control and data integration the PsA and RA cellular landscape was generated and nine mega clusters indicative of fibroblasts, endothelial cells, pericytes, macrophages, dendritic cells (DC), B cells, plasma cells, T cells and NKT consisting of several sub clusters were identified. Distinct points of transcriptomic deviation and convergence between RA and PsA were identified for each of the major cell types of the joint. Specifically, cell cycle and trajectory analysis revealed that only a fraction of synovial T cells are actively proliferating. Additionally, the differential usage of immunoglobulin light chains by memory and plasma cells indicates that plasma cells are potentially not derived from the local memory B cell pool of the synovial tissue. Importantly, we report distinct fibroblast and endothelial cell transcriptomes indicating differentially abundant subpopulations in RA and PsA characterised by distinct transcription factor usage and signalling pathway enrichment. Specifically transcriptomic imputation analysis revealed abundance of invasive FAPα+THY1+ regulated by transcription factor TEAD1 in RA compared to PsA synovial tissue. In order to identify potential cell-cell communication driving inflammation in RA and PsA, novel receptor–ligand interaction networks were generated and downstream of the receptor, target characterisation was performed. Herein we identify RA-specific synovial T cell-derived TGF-β and macrophage IL-1β synergy in driving the transcriptional profile of FAPα+THY1+ invasive synovial-fibroblasts, expanded in RA compared to PsA synovial tissue biopsies (Figure 1). Ex vivo treatment of RA patient synovial fibroblasts identified TGF-b and IL-1b synergy are a major driver of IL-6 production, fibroblast activation and adhesion molecule expression. Interestingly, the aforementioned proinflammatory changes of RA patient synovial fibroblasts were coupled with significant alterations in mitochondrial eccentricity and size and a marked metabolic adaptation towards a strongly glycolytic profile (Figure 1).

Figure 1.

Conclusion

Disrupting specific immune and stromal cell interactions offers novel opportunities for targeted therapeutic intervention in RA and PsA.

Disclosure of Interests

Achilleas Floudas: None declared, Conor Smith: None declared, Orla Tynan: None declared, Nuno Neto: None declared, Vinod Krishna Employee of: Janssen Pharmaceuticals, Sarah Wade: None declared, Megan Hanlon: None declared, Clare Cunningham: None declared, Viviana Marzaioli: None declared, Mary Canavan: None declared, Jean Fletcher: None declared, Suzanne Cole Employee of: Janssen Pharmaceuticals, Ling-Yang Hao Employee of: Janssen Pharmaceuticals, Sunil Nagpal Employee of: Janssen Pharmaceuticals, GSK, Michael Monaghan: None declared, Douglas Veale Consultant of: Janssen, Eli Lilly, Pfizer, Ursula Fearon Consultant of: Janssen, Eli Lilly, Pfizer.

AB0037 EXPRESSION OF NEGATIVE CHECKPOINT MOLECULES BTLA AND HVEM IS DYSREGULATED IN AUTOIMMUNE DISEASES

Background:

Immune checkpoint blockade with agents targeting CTLA4 and PD-1/PD-L1 alone or in combination has demonstrated exceptional efficacy in multiple cancer types by “unleashing” the cytotoxic action of quiescent, tumor-infiltrating T cells. However, the therapeutic action of these immunotherapies goes hand in hand with the loss of immune tolerance and appearance of immune-related adverse events such as colitis, arthralgia and inflammatory arthritis in responsive patients. Therefore, immune checkpoint molecules have been proposed as targets for the treatment of autoimmune diseases.

Objectives:

Herein, we interrogate the potential of BTLA/HVEM axis as a target for restoring immune homeostasis in rheumatoid arthritis (RA), Systemic Lupus Erythematosus (SLE) and Sjogren’s Syndrome (SjS) by examining their expression patterns in autoimmune disease tissues.

Methods:

Message and protein expression of BTLA and HVEM were examined in RA and SLE synovial tissues, SLE cutaneous lesions, SjS salivary glands and peripheral blood samples of autoimmune disease by RNA sequencing and flow cytometry.

Results:

Tissue dysregulation of the BTLA-HVEM axis was observed: Increased BTLA RNA level in RA synovium, SLE-affected skin, and SjS salivary gland samples, whereas HVEM level was affected only in the RA synovium when compared to unaffected tissues. Detailed immunophenotyping of B, T, and myeloid cell populations in RA, SLE, SjS and healthy control PBMCs revealed differential modulation of the BTLA+ or HVEM+ immune cell subsets in a disease-context dependent manner. SjS patients showed an overall decrease in memory B cells and most of the BTLA+ B cell subsets while a decrease in HVEM+ B cells was observed only in SLE PBMC samples and not RA and SLE samples. Immunophenotyping with a T cell panel exhibited decreased BTLA and HVEM expression on T cell subsets in SjS and SLE but not in RA patients. In addition, protein levels of HVEM were differentially decreased in SLE myeloid cell subsets. Finally, we demonstrate tissue-specific surface expression patterns of BTLA in RA and SLE samples: higher surface BTLA levels on RA and SLE PBMC B cells than matched tissue-derived B cells.

Conclusion:

Our results demonstrate a dysregulation of the BTLA/HVEM axis in either lesional tissue or peripheral blood in an autoimmune disease context-dependent manner. These results also indicate the potential of targeting BTLA-HVEM axis for the treatment of multiple autoimmune diseases.

Disclosure of Interests:

Sunil Nagpal Shareholder of: Janssen Pharmaceuticals, Employee of: Janssen Pharmaceuticals, Suzanne Cole Shareholder of: Janssen Research & Development employee, Employee of: Janssen Research & Development employee, Achilleas Floudas: None declared, Mihir Wechalekar Grant/research support from: Grant from Janssen Research & Development, Qingxuan Song Shareholder of: Employee of Janssen Research, Employee of: Employee of Janssen Research, Tom Gordon: None declared, Roberto Caricchio Grant/research support from: Financial grant from Janssen Research & Development, Douglas Veale: None declared, Ursula Fearon: None declared, Navin Rao Shareholder of: Janssen Pharmaceuticals, Employee of: Janssen Pharmaceuticals, Ling-Yang Hao Shareholder of: Employee of Janssen Research, Employee of: Employee of Janssen Research

Effects of different types of zinc supplement on the growth, incidence of diarrhea, immune function, and rectal microbiota of newborn dairy calves

Neonatal diarrhea in dairy calves causes huge economic and productivity losses in the dairy industry. Zinc is an effective anti-diarrheal agent, but high doses may pose a threat to the environment. Therefore, we aimed to evaluate the effects of low-dose zinc supplementation on the growth, incidence of diarrhea, immune function, and rectal microbiota of newborn Holstein dairy calves. Thirty newborn calves were allocated to either a control group (without extra zinc supplementation), or groups supplemented with either 104 mg of zinc oxide (ZnO, equivalent to 80 mg of zinc/d) or 457 mg of zinc methionine (Zn-Met, equivalent to 80 mg of zinc/d) and studied them for 14 d. The rectal contents were sampled on d 1, 3, 7, and 14, and blood samples were collected at the end of the study. Supplementation with ZnO reduced the incidence of diarrhea during the first 3 d of life, and increased serum IgG and IgM concentrations. The Zn-Met supplementation increased growth performance and reduced the incidence of diarrhea during the first 14 d after birth. The results of fecal microbiota analysis showed that Firmicutes and Proteobacteria were the predominant phyla, and Escherichia and Bacteroides were the dominant genera in the recta of the calves. As the calves grew older, rectal microbial diversity and composition significantly evolved. In addition, dietary supplementation with ZnO reduced the relative abundance of Proteobacteria in 1-d-old calves, and increased that of Bacteroidetes, Lactobacillus, and Faecalibacterium in 7-d-old calves, compared with the control group. Supplementation with Zn-Met increased the relative abundance of the phylum Actinobacteria and the genera Faecalibacterium and Collinsella on d 7, and that of the genus Ruminococcus after 2 wk, compared with the control group. Thus, the rectal microbial composition was not affected by zinc supplementation but significantly evolved during the calves' early life. Zinc supplementation reduced the incidence of diarrhea in young calves. In view of their differing effects, we recommend ZnO supplementation for dairy calves during their first 3 d of life and Zn-Met supplementation for the subsequent period. These findings suggest that zinc supplementation may be an alternative to antibacterial agents for the treatment of newborn calf diarrhea.

Correlation between transcription factor activator protein-2β (TFAP-2β) and endometrial carcinoma

AIMS

To investigate the correlation between transcription factor activator protein-2β (TFAP-2β) and endometrial carcinoma (EC).

MATERIALS AND METHODS

The study comprised 60 randomly selected patients diagnosed and treated at the 2nd Affiliated Hospital of Harbin Medical University from November 2011 to June 2012 for endometrial carcinoma (n = 30) and myoma of uterus (n = 30). The expression of TFAP-2Pβ mRNA in endometrial carcinoma was analyzed by real-time reverse transcription polymerase chain reaction (RT-PCR). Body mass index (BMI), waist circumference, and venous blood samples were obtained before abdominal surgery clinically.

RESULTS

The expression of TFAP-2β mRNA in endometrial tissue of patients with EC was higher than that of normal endometrium (p < 0.05). The expression of TFAP-2β mRNA in endometrial tissue of patients with metabolism syndrome was higher than that of lean ones (p < 0.05). There was no significant difference in the expression of TFAP-2β mRNA in endometrial tissue between patients with both EC and metabolism syndrome and in those with EC only. The expression levels of TFAP-2β mRNA had positive correlation with triglyceride (r = 0.271, p < 0.05) and high-density lipoprotein (HDL) (r = 0.314, p < 0.05). There was no significant correlation between the expression of TFAP-2β mRNA and CA125, fasting plasma glucose, low-density lipoprotein (LDL), waist circumference, total cholesterol, and BMI.

CONCLUSIONS

TFAP-2β constituted promoter activity in EC and also contributed to the development of the metabolic syndrome. TFAP-2β may influence the oc- currence and development of EC through regulating the expression of various adipokines and lipoprotein metabolism. Probably TFAP-2β can be a candidate tumor marker for EC.

Exogenous nitric oxide negatively regulates the S-nitrosylation p38 mitogen-activated protein kinase activation during cerebral ischaemia and reperfusion

AIMS

A number of studies have suggested that nitric oxide (NO) plays an important role in the reactive phosphorylation of p38MAPKα (p38). However, whether S-nitrosylation of p38 is activated by NO and the details remain unclear. The aim of the present work was to assess the activation of p38, the S-nitrosylation site and the p38 signalling pathway in rat hippocampus and in HEK293 cell induced by exogenous NO.

METHODS

Primary hippocampal cultures, HEK293 cells and rat model of cerebral ischaemia/reperfusion (brain ischaemia was induced by four-vessel occlusion procedure) were used in this study. Biotin-switch method and immunoblotting were performed to study the S-nitrosylation and phosphorylation of p38, and neuronal loss was observed by histology.

RESULTS

Endogenous NO increased p38 phosphorylation and S-nitrosylation, and the activation of p38 was dependent on the S-nitrosylation of Cys-211, which was critical for the NO-mediated activation of p38. The exogenous NO donor sodium nitroprusside, S-nitrosoglutathione, 7-nitroindazole, the inhibitor of the neuronal nitric oxide synthase, inhibited the activation of p38 signal pathway induced by cerebral ischaemia/reperfusion and attenuated the damage in rat hippocampal neurones. Moreover, the N-methyl-D-aspartate receptor (NMDAR) is probably involved in the p38 activation process of S-nitrosylation and phosphorylation.

CONCLUSION

Endogenous NO induces the S-nitrosylation and phosphorylation of p38 and mediates p38 signalling pathway by NMDAR, and as exogenous NO inhibits this process and is neuroprotective in rat cerebral ischaemia/reperfusion, it may make a contribution to stroke therapy.

Prenatal exposure to lipopolysaccharide results in cognitive deficits in age-increasing offspring rats

Studies have suggested that maternal infection/inflammation maybe a major risk factor for neurodevelopmental brain damage. In the present study, we evaluated the effects of prenatal exposure to a low level of inflammatory stimulation lipopolysaccharide (LPS) repeatedly on spatial learning and memory performances in rat offspring's lifetime. Sixteen pregnant Sprague-Dawley rats were randomly divided into two groups. The rats in the LPS group were treated i.p. with LPS (0.79 mg/kg) at gestation day 8, 10 and 12; meanwhile the rats in the control group were treated with saline. After delivery, the rat offspring at 3- (young), 10- (adult) and 20-mon-old (aged) were allocated. Spatial learning and memory abilities were tested by Morris water maze. The structure of hippocampal CA1 region was observed by light microscopy. The expression of synaptophysin (SYP) and glial fibrillary acidic protein (GFAP) in hippocampal CA1 region were measured by immunohistochemistry. Results showed that the rat offspring of LPS group needed longer escape latency and path-length in the Morris water maze and presented a significant neuron loss, decreased expression of SYP, increased expression of GFAP in CA1 region in histological studies. All these changes were more significant with the age increasing. These findings support the hypothesis that maternal systemic inflammation may alter the state of astrocytes in rat offspring for a long time, the alteration may affect neurons and synapse development in neural system, increase the neurons' vulnerability to environment especially as the age increasing, at last result in distinct learning and memory impairment.

The shortest telomere, not average telomere length, is critical for cell viability and chromosome stability

Loss of telomere function can induce cell cycle arrest and apoptosis. To investigate the processes that trigger cellular responses to telomere dysfunction, we crossed mTR-/- G6 mice that have short telomeres with mice heterozygous for telomerase (mTR+/-) that have long telomeres. The phenotype of the telomerase null offspring was similar to that of the late generation parent, although only half of the chromosomes were short. Strikingly, spectral karyotyping (SKY) analysis revealed that loss of telomere function occurred preferentially on chromosomes with critically short telomeres. Our data indicate that, while average telomere length is measured in most studies, it is not the average but rather the shortest telomeres that constitute telomere dysfunction and limit cellular survival in the absence of telomerase.

Calpastatin domain L is involved in the regulation of L-type Ca2+ channels in guinea pig cardiac myocytes

We have found previously that L-type Ca2+ channel run-down in cell-free patches is partially (10-28%) reversed by calpastatin (CS) and have suggested that CS, an endogenous inhibitor of calpain, has a Ca2+-channel-regulating function. CS is composed of repetitive domains 1-4 (calpain-inhibitory domain) and domain L (a domain whose function is unknown). We therefore investigated which domain of CS was involved in the regulation of Ca2+ channel activity in guinea pig cardiac myocytes using the patch-clamp technique. After the patches were excised into inside-out mode in basic internal solution, the Ca2+ channel activity ran down to 0.45% of the control level recorded in the cell-attached mode. Application of human recombinant full-length CS (25 microM) and domain L (25 microM) restored the Ca2+ channel activity to 13 and 19% of the control level, respectively, while the channel activity was not restored by CS domain 1 (25 microM) (0.66%). Mouse CS domain XLL (25 microM), a complex of domain XL and domain L, restored the calcium channel activity to 11% of the control level. These results suggested that the Ca2+ channel-regulating function of CS is located in domain L. This study is the first description of the function of CS domain L.

Effects of calcium channel blockers on calcium release-activated calcium currents in rat hepatocytes

AIM

To study the influences of calcium channel blockers on calcium release-activated calcium currents (ICRAC) in rat hepatocytes.

METHODS

Whole-cell patch-clamp technique was used.

RESULTS

The peak amplitude of ICRAC was -0.41 nA +/- 0.09 nA (n = 15), its reversal potential was about 0 mV. Verapamil (Ver), diltiazem (Dil), and nifedipine (Nif) decreased ICRAC strikingly, without affecting its reversal potential. The inhibitory rate of Ver 5 mumol.L-1 was 40% +/- 12% (n = 3), Ver 50 mumol.L-1 reduced the peak amplitude of ICRAC from -0.49 nA +/- 0.12 nA to -0.20 nA +/- 0.09 nA (P < 0.01 vs control, n = 5). The inhibitory rate was 57% +/- 15%. Dil 50 mumol.L-1 and Nif reduced ICRAC from -0.43 nA +/- 0.10 nA to -0.29 nA +/- 0.07 nA (P < 0.01 vs control, n = 5), from -0.32 nA +/- 0.08 nA to -0.27 nA +/- 0.08 nA (P < 0.01 vs control, n = 5). The inhibitory rate was 31% +/- 11%, 19% +/- 7%, respectively. The amplitude of ICRAC was dependent on extracellular Ca2+ concentration. The peak amplitude of ICRAC was -0.21 nA +/- 0.08 nA (n = 3) in Tyrode's solution with Ca2+ 1.8 mmol.L-1 (P < 0.01 vs the peak amplitude of ICRAC in external solution with Ca2+ 10 mmol.L-1).

CONCLUSION

The three calcium antagonists inhibited ICRAC effectively and protected hepatocytes from calcium overload via the inhibition of ICRAC.

A cytoplasmic factor, calpastatin and ATP together reverse run-down of Ca2+ channel activity in guinea-pig heart

1. The cytoplasmic extract of bovine heart was separated into four fractions by gel filtration: H (molecular mass > 300 kDa), P (250-300 kDa), L1 (180-250 kDa) and L2 (< 180 kDa). The effects of these fractions on the run-down of L-type Ca2+ channel activity were investigated in guinea-pig ventricular myocytes. 2. After run-down induced by inside-out patch formation, Ca2+ channel activity was restored by P or H (+ 3 mM ATP) to 7.5 and 5.8 % of that in the cell-attached mode, respectively, but to as high as 86 % by P + H + ATP. 3. The reversal of run-down brought about by the P fraction was mimicked by calpastatin. 4. The restorative effect of calpastatin + ATP showed a biphasic time course: 38 % in the early transient phase and 11 % in the late phase. However, calpastatin + H + ATP showed a sustained effect: 66 % in the early transient phase, and 87 % in the late phase. 5. The effective component of the H fraction showed a protein-like nature: heat and trypsin sensitivity. 6. The activities of cAMP-dependent protein kinase, casein kinase I, casein kinase II, protein tyrosine kinase, protein serine/threonine or tyrosine phosphatases were measured. However, these kinases and phosphatases were not confirmed as the effective component of cytoplasm or the H fraction. 7. Run-down was not prevented by 2 microM phalloidin or 2 microM paclitaxel, suggesting that neither actin filaments nor microtubules are directly involved in the run-down. 8. Our results support the view that the basal activity of the Ca2+ channel is maintained by at least three factors: a protein-like factor in the H fraction, calpastatin, and ATP.

Run-down of L-type Ca2+ channels occurs on the alpha 1 subunit

Run-down of L-type Ca2+ channels in CHO cells stably expressing alpha 1c, alpha 1c beta 1a, or alpha 1c beta 1a alpha 2 delta gamma subunits was studied using the patch-clamp technique (single channel recording). The channel activity (NPo) of alpha 1c channels was increased 4- and 8-fold by coexpression with beta 1a and beta 1a alpha 2 delta gamma, respectively. When membranes containing channels composed of different subunits were excised into basic internal solution, the channel activity exhibited run-down, the time-course of which was independent of the subunit composition. The run-down was restored by the application of calpastatin (or calpastatin contained in cytoplasmic P-fraction) + H-fraction (a high molecular mass fraction of bovine cardiac cytoplasm) + 3 mM ATP, which has been shown to reverse the run-down in native Ca2+ channels in the guinea-pig heart. The restoration level was 64.7, 63.5, and 66.4% for channels composed of alpha 1c, alpha 1c beta 1a, and alpha 1c beta 1a alpha 2 delta gamma, respectively, and was thus also independent of the subunit composition. We conclude that run-down of L-type Ca2+ channels occurs via the alpha 1 subunit and that the cytoplasmic factors maintaining Ca2+ channel activity act on the alpha 1 subunit.

Characterization and partial purification of the cytoplasmic factor that maintains cardiac Ca2+ channel activity

Using the patch clamp method we attempted to characterize the cytoplasmic factor in guinea-pig cardiac myocytes which restores L-type Ca2+ channel activity after run-down. The factor was eluted from a diethylaminoethyl (DEAE) sepharose column by KCl at 100-360 mM. On gel filtration the factor had an apparent molecular mass (Mr) of 250-300 kDa. Two-dimensional electrophoresis of the partially purified factor showed at least nine spots, of which the major spot had a Mr of about 100 kDa and an isoelectric point of 4.8, suggesting that the physicochemical properties of the factor resemble those of calpastatin, an endogenous inhibitor of Ca2+-activated protease, calpain. Calpastatin activity was increased in the partially purified cytoplasm and an antibody raised against calpastatin recognized the major band. Reduction of calpastatin in the cytoplasm decreased the potency of Ca2+ channel activation. These results suggest that calpastatin might interact with the Ca2+ channel and maintain channel activity.

Two different activities of phospholipase A2 in porcine aortic cytosol

Two different activities of phospholipase A2 (PLA2s, EC 3.1.1.4) which was activated at micro molar concentration of free Ca2+ were identified in cytosolic fraction of porcine aortic tissue. The two enzymes behaved very similarly during purification on ion-exchange, hydrophobic, gel filtration and affinity columns, and finally the active peaks of these enzymes were separated from each other on a hydroxyapatite HPLC column. Both of the enzymes hydrolyzed efficiently phosphatidylcholine (PtdCho) containing arachidonoyl residue as the substrate, but showed the apparent differences in head group specificity of phospholipids and also in the sensitivity against high Ca2+ concentration. This is the first report for the identification and characterization of high molecular weight cytosolic PLA2s in porcine aortic tissue.

Effect of dl-praeruptorin A on calcium current in ventricular cells of guinea pig

With patch clamp technic (whole cell recording), the effect of dl-praeruptorin A (Pra), an ingredient of Peucedanum praeruptorum Dunn on calcium current (ICa) in the single ventricular cells of guinea pig was studied. Results showed that under Cs/Cs condition, when the holding potential was -40 mV and in the presence of Pra (1, 10, 100 mumol.L-1), ICa was decreased dose-dependently from 2.02 +/- 0.24, 2.00 +/- 0.12, 2.12 +/- 0.33 nA (control) to 1.60 +/- 0.24, 1.32 +/- 0.08, 1.16 +/- 0.43 nA, respectively, and their inhibitory rates were 21%, 33.5%, 45%, respectively. The current-voltage relation curve showed that the reversal potential of ICa was +60 mV; the potential producing peak value of ICa was about 0 mV. The results indicated that Pra had a Ca2+ channel blocking effect.

Whole-cell patch clamp measurements and berberine inhibition of hyperpolarization-activated inward current in rabbit sinoatrial node cells

Single rabbit sinoatrial node (SAN) cells were isolated by means of an enzymatic dispersion procedure and used for the whole-cell patch clamp experiment. At a holding potential of -40 mV, a time- and voltage-dependent inward current, I(f), was activated at different hyperpolarization potentials from -60 mV to -110 mV. The current-voltage relation curve showed that I(f) was activated at potential more negative than -40 mV. Five min after treatment by CsCl 2 mmol.L-1-containing Tyrode solution, I(f) was almost completely blocked. At a hyperpolarization potential of -110 mV, I(f) was reduced from 1.7 +/- 0.2 nA of the control to 1.2 +/- 0.4 nA after superfusing with Tyrode solution containing berberine (Ber) 1 mumol.L-1 for 5 min. And it was difficult to wash out this action. Ber also had inhibitory effects on other currents to a certain extent. The results indicate that I(f) is a Cs(+)-sensitive current and that the negative chronotropic effect of Ber may be due to the inhibition of I(f) that functions as an important pacemaking modulator for the spontaneous depolarization of SAN tissue.